The proposed research is designed to elucidate some of the mechanisms which enable the food-borne pathogen Salmonella typhimurium to perform aerobic/anaerobic growth shifts. The experiments are centered around the enzyme systems involved in the anaerobic oxidation of formate and in the anaerobic production of hydrogen sulfide. These two enzyme systems are linked, and each offers certain advangages in the study of anaerobic metabolism. We plan to isolate and characterize mutants defective in the formate dehydrogenase linked to nitrate reduction (FDHN), in the formate dehydrogenase linked to hydrogen gas production (FDHH), and in thiosulfate reductase. The characterizations will involve primarily mapping experiments and electrophoretic studies of the enzyme protein isolated from the various mutants. It is expected that the resulting data will provide an understanding of the regulation of these anaerobic enzyme systems.